A conventional ultrasound imaging system, such as is used in medical imaging, for example, comprises an array of ultrasonic transducer elements which transmit an ultrasound beam and then receive the reflected beam from the object being studied. For ultrasound imaging, the array typically comprises a multiplicity of transducer elements arranged in a line and driven with separate respective voltages. By selecting the time delay (or phase) and amplitude of the applied voltages, the individual transducer elements can be controlled to produce ultrasonic waves which combine to form a net ultrasonic wave that travels along a preferred vector direction and is focused at a selected point along the beam. Multiple firings may be used to acquire data representing the same anatomical information. The beamforming parameters of each of the firings may be varied to provide a change in maximum focus or otherwise change the content of the received data for each firing, e.g., by transmitting successive beams along the same scan line with the focal point of each beam being shifted relative to the focal point of the previous beam. By changing the time delay and amplitude of the applied voltages, the beam with its focal point can be moved in a plane to scan the object.
The same principles apply when a transducer probe is employed to receive the reflected sound in a receive mode. The voltages produced at the receiving transducer elements are summed so that the net signal is indicative of the ultrasound reflected from a single focal point in the object. As with the transmission mode, this focused reception of the ultrasonic energy is achieved by imparting a separate time delay (and/or phase shift) and gain to the signal from each respective receiving transducer element.
Such scanning comprises a series of measurements in which the steered ultrasonic wave is transmitted, the system switches to receive mode after a short time interval, and the reflected ultrasonic wave is received and stored. Typically, transmission and reception are steered in the same direction during each measurement to acquire data from a series of points along an acoustic beam or scan line. The receiver is dynamically focused at a succession of ranges along the scan line as the reflected ultrasonic waves are received.
Ultrasonic imaging systems are known in which each transducer element is served by a respective individual analog channel followed by a respective analog-to-digital (or A/D) converter and one respective delay chip. Thus, a 128-channel system requires 128 delay chips and all of their associated memory and bus components.
In some ultrasound imaging systems, the number of transducer elements is greater than the number of time delay channels. For example, a system having a 256-segment transducer and a 128-channel beamformer is known. That system requires multiple firings and multiplexing of the transducer signals to provide this expanded function. Repeated firings, however, limit applicability of this technique to relatively modest increases.
With 1.5-dimensional and two-dimensional arrays planned for the future, systems utilizing a large number of effective channels will be required. This must be achieved without a concomitant increase in power and complexity. An architectural concept that can provide these results without resorting to multiple firings is required.